Thursday, March 19, 2015

Serum is the supernatant fluid when clotted blood has been centrifuged. It is the best specimen for most clinical chemistry laboratory tests because of its specific characteristics. Here are the reasons why serum is the best specimen.

*Serum has less protein

When blood clots, one of the proteins - fibrinogen - takes part in the clotting process; thereby removing it from the serum. The absence of fibrinogen would make the supernatant clearer, while in plasma, since the blood does not clot, the fibrinogen remains in the supernatant and could add to the turbidity of the plasma.

*Serum has no anticoagulant

Since serum does not have an anticoagulant, there are no other substances that could interact with your test. There are potential interferences coming from anticoagulants with certain tests.

One example is the interference of the anticoagulant ethylene diaminetetraacetic acid (EDTA) in the laboratory determination of calcium ions. EDTA chelates calcium; hence, decreasing inaccurately the concentration of calcium in the sample.

The presence of an anticoagulant could also dilute the specimen and unreliably lower the concentration of the substance being analyzed.

*Most reagents are more compatible with serum

The optimum reaction of the reagent with the substance in the blood is very important to produce reliable results; results that are precise and accurate simultaneously.

When a result is precise, it means that you get almost the same results repeatedly. Accuracy on the other hand, means obtaining values close to the “true value.”

When a result or method is reliable, then you are certain of the results because you know they could be depended on.
Laboratory results are the data that doctors could base their diagnosis on.

Together with the history of the patient, the other diagnostic results, doctors could now come up with a conclusive diagnosis.

*Serum can be more stable than plasma with certain substances

Some research like the study done by O'Keane and Cunningham proved that serum is more stable for other substances than plasma.

This is most especially for serum extracted with a separator gel. Gel tubes proved to be stable for creatinine, potassium, and urea than in plasma.

This would specify that gel tubes are more stable that plain serum tubes.
These are the reasons why serum is considered the best specimen.

This does not indicate though, that the other blood specimens could not be used. There are certain tests, which require, specifically a plasma sample or a whole blood sample.

Knowing what these tests are would help a lot in coming up with reliable results and a correct diagnosis by the doctor.

Wednesday, March 18, 2015

Ethanol is a type of alcohol that can be used as a motor fuel or fuel additive. It is also present in alcoholic beverages, scents, and is sometimes used as a recreational drug. Previous studies revealed that ethanol can be produced from lignocellulosic biomass of corn stovers.

The process was originally considered as promising. The use of supposedly “useless” agricultural by-products, like corn stovers, to produce an alternative source of motor fuel was a sensational discovery, considering the scarcity of gasoline available for worldwide consumption.

Further studies revealed however, that the production of ethanol from corn stover has been found out to waste corn because of the following reasons:

1. Ethanol combustion produces 2.14 times as much ground level ozone than gasoline
The data was presented by the Clean Fuels Report about the comparison of fuel emissions between ethanol and gasoline.

The report further stated that ethanol contributes 1.7 to the pollution caused by smog, while gasoline contributes only 1.0.

2. Prices of corn increased
Because of the increase need in the production of ethanol from corn stovers, the price of corn has actually increased in the market.

The reduced supply of corn as staple food has prompted the increase in its price, while the total cost of producing ethanol from corn has also increased. Either way, the consumers do not benefit in the end.

3. Processing of corn stovers to ethanol is costly
Contrary to previous assumptions, the production of a liter of ethanol is more costly than 1 liter of gasoline.

This is because the process of hydrolysis needs large amounts of water, needs more money to deal with carbon emissions, and requires more energy for its processing. The sugars present in the corn stovers have also to undergo fermentation before they are converted to ethanol, adding more production costs.

4. Environmental friendliness of ethanol is in question
Ethanol from corn is not altogether environmental friendly because it produces acetaldehyde and formaldehyde which are considered as harmful substances. These substances can cause cancer when persons are exposed continuously for a long period of time. They pollute the environment through the water that you drink, the air you breathe and the substances or food that you take in.

The US national budget for the production of ethanol from corn was recently slashed last June, 2011 by the US Senate because of some of these aforementioned reasons.

The corn prices have dropped since then, and with this development, the corn industry would go back to being one of the primary sources of food for humans and animals and not as a source of biofuel.

Saturday, July 19, 2014

Blood gas analysis (BGA) is also known as arterial blood gas determination (ABG), and is considered a special test in the clinical laboratory. The commonly assayed parameters are partial pressure carbon dioxide (pCO2), hydrogen ion concentration (pH) and bicarbonate (HCO3). The determination of these substances helps in the evaluation of the acid-base status of a patient.

Image credit: Lara Enriquez

The following are certain precautions observed by medical technologists in the extraction of arterial blood for blood gas analysis.

1. The best specimen is arterial blood.

This is because arterial blood is more homogenous than venous blood. The blood could be collected in the following common arterial sites: the radial artery, the brachial artery, the femoral artery and the scalp artery.

The most ideal anticoagulant is dry heparin, and the preferable syringe is a glass syringe. Recently, new receptacles are manufactured which are specifically for BGA.

2. Collect the specimen anaerobically (without air).

Your specimen should be covered at all times to prevent the escape of carbon dioxide to the air. It should be transported immediately to the testing laboratory. If it is left uncovered, unreliable results will be obtained which will lead to a wrong diagnosis by the Clinician/physician.

3. Preserve in crushed ice, if not tested immediately.

The low temperature has to be maintained. An increase in temperature would cause the gas to evaporate. It must also be preserved properly to obtain reliable results, aside from making sure that it is covered.

The body naturally maintains a state of balance called homeostasis. In the case of blood pH, this is done by the lungs and the kidneys which act as compensatory organs for one another. When the lungs are dysfunctional just like in respiratory diseases (emphysema, TB, chronic bronchitis, etc), the kidneys respond by excreting or retaining bicarbonate (HCO3).

On the other hand, when the kidneys are dysfunctional, the lung will respond by the increase retention or excretion of carbon dioxide (CO2). Through these physiologic processes, the critical pH (acidity and alkalinity) of blood is maintained at 7.35 to 7.45. Any slight variation from this pH, whether an increase or decrease, will lead to coma and eventually death. It is therefore imperative that the body maintains this slightly alkaline pH of blood for good health.

The following are acid-base conditions and the corresponding compensatory mechanisms :

Values : pH - decreased , PCO2 normal, HCO3 - decreased

Condition - metabolic acidosis

Compensatory mechanism - hyperventilation , increase excretion of CO2

decreased retention of CO2

Values: pH increased, HCO3 - increased , PCO2-normal

Condition - metabolic alkalosis

Compensatory mechanism - hypoventilation, decreased excretion of CO2

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increased retention of CO2

Values : pH- increased , PCO2 - decreased , HCO3 -normal

Condition - respiratory alkalosis

Compensatory mechanism : increased retention of HCO3

decreased excretion of H+

Values: pH-decreased , PCO2 -increased, HCO3 -normal

Condition: respiratory acidosis

Compensatory mechanism : increased retention of HCO3,

increased excretion of H+

Clinical laboratory scientists or medical technologists solve for the pH of blood making use of the

Where: pH =indicates the acidity or alkalinity of a solution (hydrogen ion concentration.

HCO3 - bicarbonate

DCO2 - dissolved carbon dioxide

TCO2 - total carbon dioxide

Normal values are:

pH = 7.35-7.45

HCO3 = 22 - 26 mmol/L

PCO2 = 35 - 35 mmHg

TCO2 = 23-27 mmol/L

Arterial blood gas has very important clinical significances. It is crucial that the Medical Technologists know the precautions and perform the determination accurately. A well performed ABG signifies a patient well served.